This invention relates to positive displacement devices such as internal combustion engines, pumps, compressors, and fluid motors.
An object of the present invention is to provide a novel form of a positive displacement device.
The key aspects of the positive displacement device include relative rotation and translation of a piston and a cylinder where the rotation accomplishes a rotary valve function and the translation accomplishes a change in chamber volume function; a means of linking the translation to the rotation; and a means of coupling the motion to an external device.
The preferred embodiment of the device has a relatively fixed piston which includes an intake port and an exhaust port; and a cylinder which rotates and translates relative to the piston. The cylinder contains a recessed volume which serves as a transfer port such that the piston intake port and the transfer port are in periodic registry during the cylinder rotation to allow fluid to enter the chamber through the intake port and transfer port. The piston exhaust port and the transfer port are also in periodic registry during the cylinder rotation to allow fluid to exit the chamber through the transfer port and the exhaust port. The volume between the piston and the cylinder creates a working chamber. The rotary valve action of the device is accomplished through the movement of the transfer port relative to the intake and exhaust ports. The translation of the cylinder relative to the piston creates the change in chamber volume.
The rotary valve action is accomplished in an alternative embodiment including a relatively fixed piston, a rotating and translating cylinder, and a relatively fixed outer case which contains the intake and exhaust ports.
The rotary valve action is also accomplished in another alternative embodiment including a relatively fixed cylinder which contains the intake and exhaust ports, and a rotating and translating piston which contains the transfer port.
The linkage between the relative rotation and translation of the piston and cylinder coordinates the expansion and compression of the working chamber with the opening and closing of the ports. The preferred embodiment of this linkage utilizes a moving cam which is attached or integral to the rotating cylinder. The moving cam is confined between two fixed cams such that as the moving cam rotates, the fixed cams cause the moving element to translate with respect to the relatively fixed element. For instance, in the preferred is embodiment, the moving cam is attached to the cylinder; and as the cylinder rotates about the piston, the moving cam rotates between the fixed cams, which creates a four-stroke translational movement of the cylinder about the piston for each revolution of the cylinder. The ability to define the rotation and translation of the cylinder enables the device to operate as a two-stroke per rotation device, a four-stroke per rotation device, or at a customized cycle such as two or more four-stroke cycles per revolution.
The ability to define the rotation and translation of the cylinder also enables the designer to minimize acceleration and deceleration forces or to create more ideal combustion cycles.
The definition of a path can be determined in alternative embodiments such as a moving cam and a fixed follower, a moving follower between fixed cams, a fixed cam and a moving follower, a lever mechanism, an electromagnetic drive, or other means.
The third aspect of this positive displacement device is a means of coupling the motion to an external device which either drives the positive displacement device or is driven by the positive displacement device. This coupling may connect only the rotational component of motion, only the translational component of motion, or both components. In the preferred embodiment of this invention, both the translation and the rotation are coupled to the external load or driver, and the means of isolating rotation and translation is external to the positive displacement device and is not included as a claimed element. In several alternative embodiments, the function of isolating either the rotational or translational component of motion is included in the device. Coupling means are well known, and include splines, spline-like devices, levers, electromagnetic means, and flexible couplings such as wafer springs, diaphragms, bellows, and coil springs.
In addition to the general aspects of rotary-valve action, linked rotation and translation, and motion coupled to an external device, some implementations of positive displacement devices require additional elements. In some applications, sealing may be provided. In some engine applications, an air/fuel mixture and an ignition source may be provided.
The preferred embodiment of the invention is a four-stroke internal combustion engine which offers substantial improvement in costs over conventional four-stroke engines and substantial improvement in emissions over conventional two-stroke engines.
The advantages of the invention over prior art can be appreciated by considering the design and function of positive displacement devices.
Many devices are used either to convert mechanical energy to gas or liquid fluid energy, or to convert fluid energy to mechanical energy. Some classes of these devices include pumps and compressors, fluid motors, and internal combustion engines. These devices can be categorized as positive displacement devices and non-positive displacement devices.
In a typical example of a positive displacement device, a working chamber changes volume through a cycle of the device. During part of the cycle, the chamber is connected to an intake by means of valves or ports, and the working fluid flows into the chamber. During another part of the cycle, the chamber is connected to the exhaust and the working fluid flows out of the chamber. In some types of positive displacement devices, closed valves or ports trap a compressible fluid in the chamber during part of the cycle, and the compressible fluid changes in volume as the volume of the chamber changes.
In the following discussion, the term xe2x80x9cload/driverxe2x80x9d refers to an external device which may either produce or sink mechanical energy. Drivers include electric motors, internal combustion engines, steam engines, water wheels, turbines, fluid motors, clock springs, and falling weights. Loads include electric generators, pumps, compressors, propellers, cranes, vehicle wheels, drills, saws, lathes, mills, and grinders. Devices for transferring energy include rotating shafts, reciprocating shafts, belts, and chains. In the positive displacement devices described by this invention, the load/driver may capture or deliver either a rotational component, a translational reciprocating component, or a combination of both the rotational and the translational components. A motor/generator is an example of the concept of the load/driverxe2x80x94it can be used as either a motor or a generator.
Three common functional classes of positive displacement devices include pumps and compressors; fluid motors; and internal combustion engines.
In a typical pump or compressor, mechanical energy from a driver such as an electric motor is used to increase the pressure or velocity of a fluid, or to reduce the volume of the fluid. Examples of these types of devices include water pumps, air compressors, refrigeration compressors and fans.
In a typical fluid motor, fluid energy is used to produce mechanical energy to a load such as a grinding wheel via a turning shaft. Examples of this type of devices include air motors, hydraulic motors, air cylinders, hydraulic cylinders, piston steam engines, and steam turbines. Fluid motors may also produce reciprocating motion as in a pneumatic chisel; or both rotating and reciprocating motion as in a hammer drill.
In a typical internal combustion engine, a chemical reaction occurs in the working fluid inside the engine thereby producing fluid energy in the form of increased pressure, volume or velocity; and that fluid energy is then converted into mechanical energy supplied to a load, such as a propeller via a turning shaft.
Mechanically, positive displacement devices can be categorized as reciprocating, rotary or hybrid.
Rotary positive displacement devices are commonly used as pumps or motors. Classes of rotary positive displacement devices include sliding vane devices and Wankel devices. In the Wankel and the sliding vane device, the boundaries of the chamber include the rotating elements and the outer case. The chamber moves with the rotary element and ports can be used for intake and exhaust of the working fluid. Drawbacks of these devices include difficulty in sealing and difficulty in cooling the rotor.
There are several disadvantages to rotary Wankel engines related to sealing. The tip seals are uncooled and unlubricated unless oil is added to the fuel. The rotor end seals require extensive machining and provide a large area for leakage, and the attempted seal against a flat area is difficult. The engines also provide a lot of area for unburned hydrocarbons to hide, which creates emissions problems. The present invention provides the advantages of a rotary valve device with the relative simplicity of sealing found in reciprocal devices.
In a typical reciprocating positive displacement device, a convex element, such as a generally cylindrical piston, reciprocates relative to a concave element, such as a hollow cylinder with one closed end. The most common reciprocating positive displacement devices use a crank and a connecting rod to couple the reciprocating motion of the piston to the rotation of a shaft. The convex element and the concave element usually have a generally round or slightly elliptical cross section, but oval cross sections and other shapes are possible.
Disadvantages of reciprocating positive displacement devices are well known and include the need for valves, which complicate the operation and add expense to the device; non-optimum piston motion due to a dependence upon a crank and rod geometry; and a requirement to compensate for side-slap oblique forces on the piston.
Typically, a sliding seal such as a piston ring is used to seal between the piston and the cylinder. Rolling seals, bellow seals, diaphragm seals and other forms of sealing have also been used. In some applications such as small model engines, the fit between the piston and the cylinder may be tight enough to limit the leakage to an acceptable amount without the use of rings or other sealing means. Some of these applications employ an interference fit to accomplish sealing.
Reciprocating positive displacement devices may have passively actuated valves, actively actuated valves, or ports. A typical four-stroke automobile engine uses actively actuated valves. An air compressor may employ reed valves that are actuated passively by the pressure of the working fluid. In other positive displacement devices, the working fluid flows into and out of the chamber by way of ports.
A typical air compressor is an example of a reciprocating positive displacement device with passively actuated intake and exhaust valves. As the chamber volume is increased, chamber pressure decreases below the pressure in the intake manifold, and the pressure difference opens the intake valve. When the volume of the chamber stops increasing, the intake valve closes. As the chamber volume is then reduced, the pressure increases above the pressure in the exhaust manifold, and the pressure difference opens the exhaust valve. Passive one way valves that require no external means of actuation can be used in an air compressor because it is desirable to have the intake valve or exhaust valve open at any time that the pressure in the chamber is less than the intake manifold pressure or greater than the pressure in the exhaust manifold.
A piston steam engine or a piston compressed air motor is an example of a reciprocating positive displacement device requiring actively actuated valves. At or near top dead center, or minimum chamber volume, the inlet valve is opened and steam or compressed air enters the chamber. At some point during the power stroke, the inlet valve is closed, and the steam or compressed air expands during the rest of the power stroke. At or near bottom dead center, the exhaust valve is opened allowing the steam or air to exhaust during the exhaust stroke.
A gasoline powered four-stroke internal combustion piston engine is another example of a reciprocating positive displacement device requiring actively actuated valves. The four-stroke engine uses two strokes, the exhaust stroke and intake stroke, to accomplish the pumping function; and two strokes, the compression stroke and power stroke, to extract energy from the working fluid by combustion. The piston reduces the chamber volume on both the compression stroke and the exhaust stroke, but the exhaust valve is opened only on the exhaust stroke. The piston increases the chamber volume on both the power stroke and the intake stroke, but the intake valve is opened only on the intake stroke. Since the exhaust valve and the intake valve are not opened or closed solely based upon the piston position, the valves are actively actuated.
A typical small gasoline powered two-stroke internal combustion piston engine is an example of a reciprocating positive displacement device with ports. Near the point in the cycle of maximum chamber volume, the intake and exhaust ports in the cylinder wall are uncovered by the piston. The intake charge mixture of air, gasoline and oil is supplied under pressure, causing the by intake charge to flow into the chamber and to displace the burned charge through the exhaust port. Ports can be used in this application because it is desirable to have the intake and exhaust ports open each time the piston nears bottom dead center and the desired open or closed state of the ports is solely a function of the piston position.
A typical hybrid positive displacement device such as a rotary-V engine or a K-cycle engine will have multiple reciprocating pistons arranged in a manner that permits ports rather than valves. The disadvantages of these devices typically include a need for sealing large surfaces, difficulty in cooling the cylinders, and that they are not suitable for single cylinder engines. The advantages of the current invention relative to other hybrid positive displacement devices include, simplicity, single cylinder embodiments, improved cooling, and easier sealing, if sealing is required.
A key feature of the present invention is the use of relative rotation and reciprocation between a cylinder and a piston. The relative rotation of the cylinder accomplishes the porting function of a rotary valve, while the relative translation accomplishes the compression, expansion, and fluid displacement functions.
The prior art indicates several engine designs involving a rotating cylinder. Most of these designs are more intricate than this invention, and most include both piston movement and cylinder movement. U.S. Pat. No. 4,136,647 which issued Jan. 30, 1979 to Stoler describes a rotary device with a pair of pistons defining a chamber particularly where the movement of the piston imparts a rotary motion to the pistons. In U.S. Pat. No. 4,553,506 which issued Nov. 19, 1985 to Prodromos Bekiaroglou et. al., there is a rotating cylinder and pistons which both rotate and reciprocate. This patent describes the use a curved guide tracks in the cylinder wall to adapt the time-law for the volume change in the working chamber to the needs of the mechanics, thermodynamics and reaction kinetics. The patent also describes a method for changing stroke length to provide variable power output. In U.S. Pat. No. 4,178,885 which issued Dec. 18, 1979 to Siegfried Konther et. al., there is a rotary piston/cylinder engine which features a crank axis offset from the axis of rotation of the cylinder. In U.S. Pat. No. 3,654,907 which issued Apr. 11, 1972 to Clarence Bartlett et. al., a rotating cylinder engine is described with relatively few moving parts. That design was said to eliminate the requirement for a muffler and to improve cooling. In U.S. Pat. No. 2,036,060 which issued Mar. 31, 1936 to Newton A. Lewis and U.S. Pat. No. 1,583,560 which issued May 4, 1926 to James K. Morris also feature rotating cylinders in rotary engines that are much different from this invention.
The prior art also indicates several engine designs involving an oscillating or reciprocating cylinder. In U.S. Pat. No. 628,124 which issued Jul. 4, 1899 to William S. Sharpneck describes an oscillating cylinder engine. In U.S. Pat. No. 4,699,093 which issued Oct. 13, 1987 to Joseph I. Byer, there is an oscillating cylinder and a fixed piston. The cylinder does not rotate.
In the present invention, the porting is accomplished by the relative rotary action of the piston and cylinder, whereas in U.S. Pat. No. 4,553,506, porting is accomplished by the relative linear motion of the piston and cylinder.
Although the art of positive displacement devices has been refined over many years, the present invention offers substantial improvements over prior art.
Although the invention may implement a four stroke cycle, it is simpler in construction than two-stroke engines. By combining rotational and translational motion, the porting and change of volume function are accomplished with the same element, and sealing, if required, is only required in one place. The invention captures the simplicity of simple 2-stroke ported devices while retaining the efficiency advantages of the more complex 4-stroke devices. As an example, the preferred embodiment of the invention is a four-stroke internal combustion engine with a single moving part.
The inherent symmetry of the invention permits efficient combinations of positive displacement devices such as an integral engine and pump which requires only one moving part. The sizes of the devices in the combination need not be the same, so the combinations may be specifically tailored for a particular application.
Despite its simplicity, the invention offers several design and operational variables to permit customization and optimization including the ability to change ignition and port timing, to dynamically vary compression ratio, to use a motion curve that minimizes acceleration and deceleration forces, to improve combustion, and to provide a movement of the combustion chamber relative to an ignition source, if ignition is used.
Internal combustion engines are typically either two-stroke engines or four-stroke engines. For small engine applications such as model engines, chain saws, lawn trimmers, leaf blowers, and off road vehicles, two-stroke engines are often employed because of their lower weight, relative simplicity, lower cost, and high power to weight ratio relative to four-stroke engines
Two-stroke engines, however, have inherently higher pollutant emissions than four-stroke engines because oil must be added to the fuel, and because the intake charge is incompletely burned. Another disadvantage of two-stroke engines is the relatively poor fuel efficiency which results from this incomplete burning of fuel. Two-stroke engines are typically run xe2x80x9crichxe2x80x9d which means that more fuel will be introduced than can be stoichiometrically combined with the oxygen provided. For instance, four-stroke engines will typically be run at air to fuel mass ratios of 13:1 is to 15:1, while two-stroke engines may be run at a ratio of 10:1. Since this ratio is substantially below the stoichiometric ratio of about 14.8:1 for gasoline, it is impossible to burn all of the fuel introduced. The results of this incomplete combustion are reduced fuel economy and increased emissions.
From the consumer""s perspective, the general advantages of four-stroke engines relative to two-stroke engines include: that there is no requirement to add oil to the fuel, that the smell is not as bad, that the engines are less noisy, that the engines are easier to start, that the engines provide better low-end torque, and that the engines run better at idle.
Four-stroke engines have improved emissions relative to two-stroke engines because they do not require the addition of oil to the fuel, and because they have more complete combustion. On the other hand, four-stroke engines typically require more moving parts than two-stroke engines.
For the foregoing reasons, there is a need for a simple, low cost, four-stroke engine. The preferred embodiment of this invention is a four-stroke ported internal combustion engine. The preferred embodiment provides a four-stroke engine with one moving part, and few parts that require machining. In this embodiment, a cam means is used to link the rotation and translation of the cylinder relative to a generally fixed piston; and the rotation accomplishes the functions of a rotary valve, while the translation accomplishes the change of volume function. A transfer port, which is a recess in the cylinder wall, provides a path for intake of fuel and air through the intake port, as well as exhaust of combustion products through the exhaust port.
The other engine embodiments of this invention offer similar advantages over prior art. These other embodiments include applications with two or more cylinders, fixed cylinder variations where the piston rotates and reciprocates relative to the cylinder, and applications where a cylinder may reside within an outer casing.
The following discussion relates to design considerations and to inherent advantages for engines and other positive displacement device embodiments of this invention.
Conventional engine design factors of compression ratio, clearances, and timing provide a starting point for setting design factors in the current invention. These factors should be viewed only as starting points because of the differences in this invention and conventional engines. The design factors may be varied in this invention just as in conventional devices depending upon the desired goals of performance, desired performance range, emissions, runnability, and fuel economy. Many of these design factors have a broader range in the current invention than is permissible in conventional devices. For example, overlap of port opening times may not be required in the invention and clearances may be smaller than in conventional engines.
Variable compression can be accomplished by such means as a motor and lead screw which move the piston, a cam, or a cam means relative to the cylinder; or by other means such as springs of appropriate stiffness or gas pressure. Thus in some applications, it may be desirable to permit some movement of the piston, so the piston is described as being relatively fixed with respect to the cylinder. Alternately, some clearance may be designed into the cam system so that the cylinder does not make the full stroke during compression at full throttle and low engine speed. This clearance provides a lower compression ratio at starting and low speeds, and a higher compression ratio as the engine speed increases. In a typical internal combustion engine, a greater clearance is present around the piston edges near the top of the piston than on the sides of the piston. One reason for providing this additional clearance is to compensate for the differential heating of the piston relative to the cylinder, which may have the benefit of air or water cooling of the cylinder block. Another reason for providing this additional clearance is to compensate for the fact that, even if the temperatures and thermal expansion coefficients were equal in the piston and cylinder, the bore of the cylinder has less thermal expansion than the piston. In the current invention, the cylinder may be thin-walled, and cooling may be provided to the piston; so a lower clearance between the top edge of the piston and the cylinder may be employed. One practical benefit of being able to reduce that clearance is that the clearance volume can be a significant source of unburned fuel. By reducing the clearances, the amount of this potential unburned fuel can be reduced substantially.
In a conventional valved four-stroke engine, the time required to open the valves is large relative to the total time required for the piston to complete a cycle. It is often necessary to begin opening the intake valve before the exhaust valve is completely closed. This overlap of times when both valves are partially open can be the source of emission of unburned fuel. The overlap also contributes to variations in the residual gas fraction which in turn contributes to cycle-to-cycle variation. It has been reported in the literature that a 10% improvement in engine power could be realized without increase in fuel consumption if cycle-to-cycle variation were eliminated. In the current invention, this overlap can be reduced or eliminated if desired.
The path of the cylinder, the size and position of the transfer port, the size and position of the exhaust port, and size and position of the intake port control the timing of the engine. The port timing may be dynamically adjusted in some embodiments by rotating the piston. This adjustment will change both the intake and the exhaust timing.
The present invention has a reduced number of moving parts relative to conventional four- stroke internal combustion engines. For instance, a two cylinder engine requires only a single moving part. The engine requires no valves. The simplicity of the design may permit ceramics or other advanced materials to be practically employed as engine construction materials. In the preferred embodiment, there are no inertial loads on the piston, so the piston is a good candidate for ceramic materials. In this invention, machining may be necessary on the inside of the cylinder and the outside of the piston. Machining may also be necessary for the cam or gear teeth in some embodiments. In the preferred embodiment, it is possible that the piston and cylinder would be die cast and that the fixed cams would be injection molded; with the outer surface of the piston and the inner surface of the cylinder being the only machined surfaces.
The operating speed of an engine can be limited by the time required to achieve combustion. Turbulent flow in the combustion chamber is necessary in all but the slowest turning engines. Turbulence is often created by swirl and squish. The swirl is achieved by techniques such as an axial introduction of fuel that creates a swirling rotational motion within the combustion chamber. In many engine designs, a squish component is created by forcing the compressed fuel and air through a relatively narrow opening. The present invention creates swirl during the intake stroke due to the relative rotation between the piston, cylinder, and ports; and creates squish during the compression stroke due to the small piston to cylinder clearance at minimum chamber volume. The invention also operates such that the charge may be moving relative to the ignition source to allow multiple ignition events along the path of the ignition source relative to the chamber, and thus creating a greater combustion efficiency. The present invention also offers an inherent squish between the chamber and the transfer port. These turbulence promoting features may enable the present invention to operate at relatively high rpm.
In some engine applications, the ignition source will ignite the fuel mixture in the transfer port, which will serve as a prechamber. The advantage of prechambers in improving combustion are well known. The shape of the transfer port in the preferred embodiment is rectangular, but the shape may be modified in all three dimensions due to considerations such as gas transfer, combustion efficiency, or the formation of a jet of burning gas.
The invention produces a high displacement to engine volume ratio which may complete a full Otto cycle in a single revolution of the cylinder. The strokes corresponding to Intake, Compression, Power, and Exhaust, are accomplished as a cylinder rotates and reciprocates about the relatively fixed piston. The present invention provides an opportunity to operate at a cycle that is closer to an idealized Otto Cycle because the path of the cylinder to piston movement can be established to achieve a cycle closer to the ideal constant volume combustion assumption in an ideal Otto cycle. The present invention also permits operation at other cycles such as the diesel cycle.
The engine may have multiple pistons arranged in a manner that share one or more cylinders. For instance a typical xe2x80x9ctwo cylinderxe2x80x9d engine, could consist of two pistons sharing a single cylinder where the closed end of the cylinder is a common wall between pistons. The wall may have cooling passages. In this case, the second piston would be rotated approximately 90 degrees, and would be upside down, with respect to the first piston.
In the four-stroke engine, the four-strokes may take place in either a single revolution or a portion of a revolution of the cylinder where there are four or more cylinder translation movements per revolution. In combinations of devices, one device may operate at a different number of cycles per revolution than other devices. For instance in the combined pump and engine example below, the engine completes four stroke per revolution of one engine cycle, while the pump completes two pump cycles in that same revolution,
One difference between an engine and other positive displacement devices is that in an engine, a chemical reaction takes place with the fluid. That reaction is usually between the oxygen in air and a fuel that is supplied. The intake charge may be a premixed fuel-air charge. Alternatively, the fuel may be introduced by port injection or direct injection. Alternately, a self reacting working fluid such as a mixture of air and solvent fumes; hydrogen and chlorine; or ethylene and a polymerization initiator may be externally supplied.
The engine may include a means to ignite the contents of the combustion chamber such as spark ignition or glow plug ignition. Alternately, the compression ratio and the fuel may be selected such that the fuel ignites spontaneously upon compression.
The combustion chamber is defined by the volume between the closed end of the cylinder and the top of the piston, as well as an additional volume in the transfer port. As the combustion chamber contents are compressed, there is only a small volume between the closed end of the cylinder and the top of the piston, and much of the fuel mixture has been compressed into the volume of the transfer port. In some embodiments, it may be desirable to increase the volume of the combustion chamber by changing the geometry of the piston face.
The transfer port permits the invention to work as a rotary valve. It may be designed as a cavity or protrusion in a portion of the wall of a rotating cylinder; a recess in a rotating piston, or as a hole in a rotating cylinder which is located within a ported outer case. In each embodiment, this port serves the function of making a connection between the working chamber and the intake and exhaust ports at various portions of the cycle.
The positive displacement devices described below include a means of defining a relative path of rotation and translation of the cylinder and the piston. The path of the rotation and translation causes the transfer port to move across the intake port and exhaust port at the time in the cycle appropriate for intake and exhaust. At other times in the cycle, the path of the cylinder is causing compression of the fuel mixture and is permitting a power stroke expansion after ignition of the compressed fuel mixture.
One way to accomplish the path definition is by use of a cam means. Several implementations of cam means are described in the embodiments. The shape of the cam means could be sinusoidal, but alternative or customized shapes may be appropriate for some applications. For instance, a modified constant acceleration cam shape can be used to lower the peak acceleration and deceleration forces and to achieve more time at the minimum chamber volume. The decrease in peak acceleration may be accompanied by a more ideal combustion cycle. Modifications of the cam shape may also lead to reduced vibration in the devices and to improved combustion.
In devices that are started by hand power or foot power such as a lawnmower, a hand held appliance, or a motorcycle, the torque required to overcome compression is often substantial. A compression release is often needed. In this invention, the compression release may be accomplished passively because of the clearance that may be designed into the cam system. The fixed cam embodiments of the present invention provide reduced inertial resistance at low rpm so that the device may be easier to start. In other embodiments, a variable compression ratio permits easier starting through a release of compression on starting the engine.
The engine may include a means to seal the combustion chamber such as a standard piston ring below the ports, above the ports, or both above and below the ports. Alternately, the piston may be designed with relatively tight tolerances without a means of sealing. In this case the fit is close enough that the leakage or blow-by is limited to an acceptable amount.
Another advantage of the invention is the elimination of side-slap forces which occur in crank engines due to the fact that the force exerted on the piston by the rod is not always aligned with the cylinder.
The present invention has improved lubrication relative to conventional devices because there is no point of zero relative motion between the cylinder and the piston. In a typical engine, the top dead center and bottom dead center locations in the cycle represent times where there is no relative motion between the piston and cylinder to promote hydrodynamic lubrication. At these times, only boundary lubrication is present.
In some embodiments, the intake charge may be directed to the inlet port through a fixed outer case, and the exhaust may be directed from the outlet port to the fixed outer case. The cylinder then contains a transfer port cavity such that as the cylinder rotates and translates relative to the piston, the intake charge is directed from the inlet port to the combustion chamber, and the exhaust is directed from combustion chamber to the exhaust port. In many applications, the engine will be incorporated into a larger product or device, and the support and enclosure functions will be provided by the larger device rather than being a part of the engine.
Heat fins may be provided to enhance the cooling of the engine or to add stiffness to the cylinder. The ability to control the temperature of the piston also offers the ability to reduce clearances between the piston and the cylinder. The ability to control the piston temperature can also make it possible to employ a ringless design. Since there is no inertial loading of the piston, it is also possible to construct the piston from higher temperature materials such as ceramics.
The means of coupling the positive displacement device to an external load/driver can be located internal or external to the positive displacement device. Some applications such as a hammer drill might use both the translational and the rotational components of the cylinder motion. In most applications only one component of the motion will be coupled to the load/driver. The means of coupling only one component of the motion include a spline, a spline-like device, a flexible coupling, and other means. A spline-like device is a device comprising a male element and a female element, with the female element overlapping the male element. The shapes of which allow relative translation but which limit relative rotation between the male and the female element. The rotational component can also be captured directly from the cam by means of gear teeth to drive a power take off gear for transferring power into or out of the engine.
The power output of the engine embodiments may be controlled by throttling air/fuel flow, by changing ignition timing, or by other standard techniques such as changing the air/fuel ratio.
In this description, terms such as top, and clockwise are intended for illustration and explanation only, and the devices can operate in any orientation. The examples shown include common techniques for which those skilled in the art recognize interchangeableness of other elements. Many other variations, modifications and applications of the illustrated embodiments of the invention will be apparent to those skilled in the art. For internal combustion engines, a good reference for design techniques and interchangeableness is the text Introduction to Internal Combustion Engines by Richard Stone, published by the Society of Automotive Engineers. Another good engine reference is Internal Combustion Engines by Colin R. Ferguson, published by John Wiley and Sons. A good metals reference is Metals Handbook published by the American Society for Metals. A good sealing reference is Seals and Sealing Handbook by Melvin W. Brown published by Elsevier Science Publishers Limited. A good coupling reference is W. W. Berg, Inc.""s B97 Master Catalog of mechanical components, including its xe2x80x9cGuide for Coupling Selectionxe2x80x9d.
This invention is a positive displacement device that can be used in engines, pumps, compressors, motors and other positive displacement device applications. The device is simple, relatively small for its displacement, and low cost. The preferred embodiment presented is a single cylinder, four-stroke internal combustion engine which comprises a cylindrical piston and a cylinder that rotates and reciprocates with respect to the piston. As the cylinder completes a revolution around the piston, a cam integral to the cylinder rotates through fixed cams and causes the cylinder to reciprocate through exhaust, intake, compression, and power strokes relative to the piston. These strokes correspond generally to the four-strokes of a conventional engine. A transfer port within the cylinder facilitates the intake of fuel and the exhaust of combustion products. The cylinder may include a cam and followers to control the cylinder movement.